The aim of this research is the understanding of the structural consequences of covalently bound carbohydrate in glycoproteins and the elucidation of the structure and function of a glycoperoxidase in biological halogenation. It is proposed that the structure of the glycosylated ribonuclease B and chloroperoxidase will be determined by single crystal X-ray diffraction and that the solution small-angle X-ray scattering of ribonuclease and hen egg-white alpha-lactalbumin will be measured under a variety of conditions. The results of the first aspect of the proposed experiments should be useful for modeling the iodination of tyrosine in the biosynthesis of thyroxin and lead to a general understanding of enzymatic peroxidation. The results of the second aspect of the proposed research will be useful in understanding the role which glycoproteins play in membrane assembly, cellular adhesion, protein-turnover, and the other physiological functions in which they are involved.